After going through a very similar situation this summer I can say verify your relays are still good. Hell if any question replace them, they are about $5 a pop at autozone. Maybe whatever was shorting and causing the fuse blow also gave the relay a hit as well.
Here's my situation. Long winded, dont read any further if you bore easily.
Driving along and out of the blue the engine died. Pulled it to the side and tried to start it, it just cranked and cranked, never started. Much like you I looked at fuses and noticed the ECC fuse blown. Replaced it and the truck fired right up. Drove about a block then it died again, sure enough fuse was blown. Getting frustrated because I could not find the problem, got it to a shop. $100 later find out a harness was rubbing somewhere which was causing the short.
Got everything fixed and the truck ran great for a few weeks then it started getting buggy again. Would start and run fine all the way home from work. Leave again, say an hour later, and the truck will not start again. Same symptoms as the burnt fuse but the fuse was fine. Started playing a swap game with the ECC relay, swapped it out for I think the blower relay...whichever had the same number, and she fired right up again.
This cycle of relay swapping went on for weeks before I just coughed up the cash for some new relays, think I replaced them all, as the blower motor was giving me hell last winter as well. Since replacing them have not had a no start, and my heat has been good all winter so far.